Vehicle Loop Sensor Installation Precautions

Precautions for burying the vehicle loop detector

The "ground sense coil" in the parking lot system is an oscillator circuit. It is constructed like this. First, create a circular groove on the ground with a diameter of about 1 meter, or a rectangular groove with a similar area, and then embed two to three turns of wire in this groove, which constitutes a An inductance coil buried on the surface is provided. This coil is a part of an oscillation circuit. It and a capacitor form an oscillation circuit. The principle is that the oscillation is stable and reliable. Measure the frequency of this oscillator. When there is a large metal object such as a car passing by, the oscillation frequency changes due to the change of the space medium (the oscillation frequency increases when there is a metal object), this change is used as a confirmation signal that the car has passed the "ground sensing coil", and this The time interval between the start and end of the signal can in turn be used to measure how fast the car is moving. This is the "ground sense coil". The technical key is that the designed oscillator is stable and reliable, and the frequency changes obviously when a car passes by.

• 1. Coil material

In the design process, only the perimeter and the number of turns of the ground induction coil are usually considered, and the material used for it is often ignored by designers. When the project is in the implementation stage, the mechanical strength and high and low temperature aging resistance of the wire must be considered. In some places with harsh environments, acid and alkali corrosion resistance must also be considered. However, in actual use of conventional wires, once the wires are aged or the tensile strength is insufficient and the wires are damaged, the detector will not work properly. Therefore, it is recommended to use Teflon high temperature multi-strand flexible conductors above 1.0mm.

• The shape of the coil

1. Rectangular installation

Usually the detection coil should be rectangular. The two long sides are perpendicular to the movement direction of the metal object, and the distance between them is recommended to be 1 meter. The length of the long side depends on the width of the road, usually the ends are 0.3 to 1 meter narrower than the road spacing.

2. 45° inclined installation

In some cases, when it is necessary to detect bicycles or motorcycles, it can be considered that the coil is installed at an angle of 45° to the driving direction.

3. "8" shape installation

In some cases, when the road surface is wide (more than six meters) and the chassis of the vehicle is too high, this type of installation can be used to disperse the detection points and improve the sensitivity. This type of installation can also be used for the detection of sliding doors, but the coil must be close to the sliding door.

• The number of turns of the coil

In order to make the detector work in the best condition, the inductance of the coil should be kept between 100uH-300uH. When the coil inductance is constant, the number of turns of the coil has an important relationship with the circumference. The smaller the circumference, the more turns. Generally refer to:

Since there may be various metal materials such as cable pipelines, steel bars, and sewer covers buried under the road, these will have a great impact on the actual inductance value of the coil, so the data in the above table is only for user reference. In actual construction, the user should use the inductance tester to actually test the inductance value of the ground induction coil to determine the actual number of turns in the construction, as long as the final inductance value of the coil is within a reasonable working range (such as between 100uH-300uH).

• 4. Output lead

When winding the coil, leave enough length of wire to connect to the loop inductor without a connector in between. After the coil cable is wound, the outgoing cable must be made into a tightly twisted pair, requiring at least 20 twists per meter. Otherwise, the untwisted output leads will introduce interference and make the coil inductance unstable. The output lead length should generally not exceed 5 meters. Since the sensitivity of the detection coil decreases with the length of the lead, keep the lead cable as short as possible.

• Burying method

To embed the coil, first use a road cutter to cut a groove on the road surface. Make 45-degree chamfers on all four corners to prevent sharp corners from damaging the coil cable. The groove width is generally 4mm~8mm, and the depth is 30mm~50mm. Also cut a slot for the coil leads to the curb. But pay attention: the groove must be clean without water or other liquids infiltrating. When winding the coil, the coil must be straightened, but not too tight and close to the bottom of the slot. After the coil is wound, the twisted output leads are drawn out through the lead-out slot.

Note: The sensitivity of the vehicle detector coil decreases with the increase of the lead length, so the length of the lead cable should be as short as possible (generally should not exceed 5 meters). The inductance value becomes unstable causing the vehicle detector to fail.

During the winding process of the coil, an inductance tester should be used to actually test the inductance value of the ground induction coil, and ensure that the inductance value of the coil is between 100uH-300uH. Otherwise, the number of turns of the coil should be adjusted. After the coil is buried, in order to strengthen the protection, a nylon rope can be wound around the coil. Finally, seal the groove with bitumen or soft resin.

地感线圈埋设注意事项

   停车场系统里“地感线圈”就是一个振荡电路。它是这样构成的，在地面上先造出一个圆形的沟槽，直径大概1米，或是面积相当的矩形沟槽，再在这个沟槽中埋入两到三匝导线，这就构成了一个埋于地表的电感线圈，这个线圈是一个振荡电路的一部分，由它和电容组成振荡电路，其原则是振荡稳定可靠，这个振荡信号通过变换送到单片机组成的频率测量电路，单片机就可以测量这个振荡器的频率了。当有大的金属物如汽车经过时，由于空间介质发生变化引起了振荡频率的变化（有金属物体时振荡频率升高），这个变化就作为汽车经过“地感线圈”的证实信号，同时这个信号的开始和结束之间的时间间隔又可以用来测量汽车的移动速度。这就是“地感线圈”。技术关键是设计出的振荡器稳定可靠并且有汽车经过时频率变化明显。

   一、线圈材料

   在设计过程中，通常仅仅考虑地感线圈的周长和匝数，对其使用什么材质常常被设计人员忽视。当工程进行到实施阶段，必须要考虑导线的机械强度和高低温抗老化问题，在某些环境恶劣的地方还必须考虑耐酸碱腐蚀问题。然而常规的导线在实际使用中，导线一旦老化或抗拉伸强度不够导致导线破损，则检测器将不能正常工作。因此建议采用1.0mm以上铁氟龙高温多股软导线。

   二、线圈形状

   1.矩形安装

   通常探测线圈应该是长方形。两条长边与金属物运动方向垂直，彼此间距推荐为1米。长边的长度取决于道路的宽度，通常两端比道路间距窄0.3米至1米。

   2.倾斜45°安装

   在某些情况下需要检测自行车或摩托车时，可以考虑线圈与行车方向倾斜45°安装。

   3.“8”字形安装

   在某些情况下，路面较宽(超过六米)而车辆的底盘又太高时，可以采用此种安装形式以分散检测点，提高灵敏度。这种安装形式也可用于滑动门的检测，但线圈必须靠近滑动门。

   三、线圈的匝数

   为了使检测器工作在最佳状下，线圈的电感量应保持在100uH-300uH之间。在线圈电感不变的情况下，线圈的匝数与周长有着重要关系。周长越小，匝数就越多。一般可参照：

   由于道路下可能埋设有各种电缆管线、钢筋、下水道盖等金属物质，这些都会对线圈的实际电感值产生很大影响，所以上表数据仅供用户参考。在实际施工时用户应使用电感测试仪实际测试地感线圈的电感值来确定施工的实际匝数，只要保证线圈的最终电感值在合理的工作范围之内(如在100uH-300uH之间)。

   四、输出引线

   在绕制线圈时，要留出足够长度的导线以便连接到环路感应器，又能保证中间没有接头。绕好线圈电缆以后，必须将引出电缆做成紧密双绞的形式，要求最少1 米绞合20次。否则，未双绞的输出引线将会引入干拢，使线圈电感值变得不稳定。输出引线长度一般不应超过5米。由于探测线圈的灵敏度随引线长度的增加而降低，所以引线电缆的长度要尽可能短。

   五、埋设方法

   线圈埋设首先要用切路机在路面上切出槽来。在四个角上进行45度倒角，防止尖角破坏线圈电缆。切槽宽度一般为4mm~8mm，深度30mm~50mm。同时还要为线圈引线切一条通到路边的槽。但要注意：切槽内必须清洁无水或其它液体渗入。绕线圈时必须将线圈拉直，但不要绷得太紧并紧贴槽底，将线圈绕好后，将双绞好的输出引线通过引出线槽引出。

   注意：车辆检测器线圈的灵敏度随引线的长度增加而降低，所以引线电缆的长度要尽可能短（一般不应超过5米），未双绞的输出引线必会引起串扰，使车辆检测器线圈电感值变的不稳定致使车辆检测器出错。

   在线圈的绕制过程中，应使用电感测试仪实际测试地感线圈的电感值，并确保线圈的电感值在在100uH-300uH之间。否则，应对线圈的匝数进行调整，在线圈埋好以后，为了加强保护，可在线圈上绕一圈尼龙绳。最后用沥青或软性树脂将切槽封上。